If you watch closely that is a light and it is streaking in the opposite direction from which the camera is moving. So camera is moving right to left. That streak is 'moving' left to right.
Obviously it's actually stationary. But it looks like it's moving because of the camera frame rate, etc.
He would have to have gone in sideways. Nearly 90 degrees bank angle. Otherwise there would be a wider swath of damage to the trees due to props. That is a narrow slice.
You can do an aileron roll in pretty much any aircraft. Now trying to recover from said aileron roll is another thing entirely. In the Q400 with only him on board? Sure. But he's going to lose a lot of altitude which is exactly what happened.
What you have to understand is that in an aileron roll the aircraft rolls around the longitudinal (horizontal) axis. This aircraft is not designed to do that maneuver so it would be slow and clunky, thus the loss of altitude.
Lastly, knock off the ridiculous 'not in an unpressurized' aircraft BS. The only reason they pressurize an aircraft is because it will fly high enough that passengers and crew would require supplemental oxygen. So they pressurize to around 8000' for comfort and to maintain a breathable atmosphere. Has nothing to do with structural integrity of the aircraft.